Java基础篇：流程控制语句，和算法应用

cicadasmile · cicadasmile · commit 23327fb4dd70 · 2020-07-26T21:29:20.000+08:00
diff --git a/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process01.java b/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process01.java
@@ -0,0 +1,45 @@
+package com.data.type.block03process;
+
+/**
+ * if...else 流程控制
+ */
+public class Process01 {
+    public static void main(String[] args) {
+        // 演示：Node01
+        if (compare01(40,30)){
+            System.out.println("40>30:true");
+        } else {
+            System.out.println("40>30:false");
+        }
+        // 演示：Node02
+        if (compare01(10,20) && compare01(20,30)){
+            System.out.println("条件成立");
+        } else {
+            System.out.println("条件不成立");
+        }
+        // 演示：Node03
+        if (compare01(20,10) || compare01(20,30)){
+            System.out.println("条件成立");
+        } else {
+            System.out.println("条件不成立");
+        }
+        // 演示：Node04
+        if(compare02(1,1))
+            if(compare02(2,2))
+                System.out.println("Running...");
+        // 演示：Node05
+        if(compare01(1,2))
+            if(compare01(5,3)){
+                System.out.println("5>3");
+            }
+    }
+
+    private static boolean compare01 (int num1,int num2){
+        System.out.println("判断：num1="+num1+";num2="+num2);
+        return num1 > num2 ;
+    }
+    private static boolean compare02 (int num1,int num2){
+        System.out.println("判断：num1="+num1+";num2="+num2);
+        return num1 == num2 ;
+    }
+}
diff --git a/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process02.java b/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process02.java
@@ -0,0 +1,24 @@
+package com.data.type.block03process;
+
+/**
+ * else...if 语句
+ */
+public class Process02 {
+    public static void main(String[] args) {
+        elseIf(11) ;
+        elseIf(9) ;
+        elseIf(5);
+    }
+
+    private static void elseIf (Integer num){
+        if (num > 10){
+            System.out.println("num > 10");
+        } else if (num > 7){
+            System.out.println("num > 7");
+        } else if (num > 4){
+            System.out.println("num > 4");
+        } else {
+            System.out.println("num < 4");
+        }
+    }
+}
diff --git a/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process03.java b/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process03.java
@@ -0,0 +1,45 @@
+package com.data.type.block03process;
+
+import java.util.Scanner;
+
+/**
+ * Switch 语句
+ */
+public class Process03 {
+
+    public static void main(String[] args) {
+        Scanner scan = new Scanner(System.in);
+        System.out.print("What day is it today：");
+        String value = scan.next();
+        weekInfo(value);
+    }
+
+    private static void weekInfo (String value){
+        switch (value) {
+            case "Monday":
+                System.out.println("Monday");
+                break;
+            case "Tuesday":
+                System.out.println("Tuesday");
+                break;
+            case "Wednesday":
+                System.out.println("Wednesday");
+                break;
+            case "Thursday":
+                System.out.println("Thursday");
+                break;
+            case "Friday":
+                System.out.println("Friday");
+                break;
+            case "Saturday":
+                System.out.println("Saturday");
+                break;
+            case "Sunday":
+                System.out.println("Sunday");
+                break;
+            default:
+                System.out.println("Matching failure");
+                break;
+        }
+    }
+}
diff --git a/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process04.java b/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process04.java
@@ -0,0 +1,33 @@
+package com.data.type.block03process;
+
+/**
+ * for 循环
+ */
+public class Process04 {
+    public static void main(String[] args) {
+        // Node01
+        int sum = 0;
+        for(int i=1; i<=100; i++) {
+            sum += i;
+        }
+        System.out.println(sum);
+
+        // Node02
+        String[] nameArr = {"Java","C++","C#"} ;
+        for (String name:nameArr){
+            System.out.println("name="+name);
+        }
+
+        // Node03
+        // 输出 i = 13
+        int i = 0;
+        for (i++; i++ < 10; i++);
+        System.out.println(++i);
+
+        // 输出：j=3 6 9
+        int j = 0;
+        for (j++; j++ < 10; j++){
+            System.out.println(++j);
+        }
+    }
+}
diff --git a/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process05.java b/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process05.java
@@ -0,0 +1,23 @@
+package com.data.type.block03process;
+
+/**
+ * while 和 do while
+ */
+public class Process05 {
+    public static void main(String[] args) {
+        int num1 = 1;
+        int num2 = 1;
+
+        // while循环
+        while(num1 <= 3) {
+            System.out.println("num1 == " + num1);
+            num1++;
+        }
+
+        // do...while循环
+        do {
+            System.out.println("num2 == " + num2);
+            num2++;
+        } while(num2 <= 3);
+    }
+}
diff --git a/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process06.java b/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process06.java
@@ -0,0 +1,31 @@
+package com.data.type.block03process;
+
+/**
+ * Return 语句
+ */
+public class Process06 {
+    public static void main(String[] args) {
+        System.out.println(getNum1());
+        System.out.println(getNum2());
+    }
+    public static int getNum1 (){
+        int a =100;
+        try{
+            return a+1;   // 这里是运算逻辑，非赋值
+        }catch(Exception e){
+            e.printStackTrace();
+        }finally{
+            return a;
+        }
+    }
+    public static int getNum2 (){
+        int a =100;
+        try{
+            return a++;   //  a++ -> a=a+1 此时a的值改变
+        }catch(Exception e){
+            e.printStackTrace();
+        }finally{
+            return a;
+        }
+    }
+}
diff --git a/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process07.java b/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process07.java
@@ -0,0 +1,15 @@
+package com.data.type.block03process;
+
+/**
+ * break 语句
+ */
+public class Process07 {
+    public static void main(String[] args) {
+        for (int i = 1 ; i < 3 ; i++){
+            if (i == 2){
+                break ;
+            }
+            System.out.println("i = " + i);
+        }
+    }
+}
diff --git a/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process08.java b/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process08.java
@@ -0,0 +1,15 @@
+package com.data.type.block03process;
+
+/**
+ * Continue 语句
+ */
+public class Process08 {
+    public static void main(String[] args) {
+        for (int i = 1 ; i < 3 ; i++){
+            if (i == 1){
+                continue ;
+            }
+            System.out.println("i = " + i);
+        }
+    }
+}
diff --git a/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process09.java b/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process09.java
@@ -0,0 +1,23 @@
+package com.data.type.block03process;
+
+public class Process09 {
+    public static void main(String[] args) {
+        int[] score = {9,8,7,6,5} ;
+        // 排序次数：最多 length - 1 次
+        for (int i = 0 ; i < score.length -1 ; i ++){
+            // 当前排序的集合区间,排序完一个数据就放弃一个
+            for (int j = 0 ; j < score.length - i - 1 ; j++){
+                // 冒泡排序：把结果大的向后扔
+                if (score[j] > score[j+1]){
+                    int temp = score[j] ;
+                    score[j] = score[j+1] ;
+                    score[j+1] = temp ;
+                }
+            }
+        }
+        // 输出排序后的结果集
+        for (int i = 0 ; i < score.length ; i++){
+            System.out.print(score[i]);
+        }
+    }
+}
diff --git a/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process10.java b/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process10.java
@@ -0,0 +1,31 @@
+package com.data.type.block03process;
+
+/**
+ * 排列组合
+ */
+public class Process10 {
+    public static void main(String[] args) {
+        arrange() ;
+    }
+    /**
+     * 有1、2、3、4个数字，能组成多少个互不相同且无重复数字的三位数？都是多少？
+     */
+    public static void arrange (){
+        int i=0; // 百位数
+        int j=0; // 十位数
+        int k=0; // 个位数
+        int t=0; // 计数器
+        for (i = 1 ; i <= 4 ; i++){
+            for (j = 1 ; j <= 4 ; j++){
+                for (k = 1 ; k <=4 ; k++){
+                    if (i != j && j != k && k != i){
+                        t += 1 ;
+                        System.out.print(i*100+j*10+k+"--");
+                    }
+                }
+            }
+        }
+        System.out.println();
+        System.out.println("t="+t);
+    }
+}
diff --git a/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process11.java b/java-se-base-parent/model-data-type/src/main/java/com/data/type/block03process/Process11.java
@@ -0,0 +1,48 @@
+package com.data.type.block03process;
+
+/**
+ * 递归算法
+ */
+public class Process11 {
+    public static void main(String[] args) {
+        System.out.println(getSumOne(100));
+        System.out.println(getSumTwo(30));
+        System.out.println(getSumThree(5));
+    }
+    /**
+     * 使用递归的方式计算1+2+...+100
+     */
+    public static int getSumOne (int i){ // 传入100
+        int sum ;
+        if (i == 1){
+            return 1 ;
+        }
+        else {
+            sum = i + getSumOne(i - 1) ;
+        }
+        return sum ;
+    }
+    /**
+     * 一列数的规则如下: 1、1、2、3、5、8、13、21、34...
+     * 求第30位数是多少， 用递归算法实现
+     */
+    public static int getSumTwo (int i){ // 传入第几位数下标
+        if (i <= 0){
+            return 0 ;
+        } else if (i == 1 || i == 2){ // 处理前面2位的1,1
+            return 1 ;
+        } else { // 当前位数是前两位之和
+            return getSumTwo(i - 1) + getSumTwo(i - 2) ;
+        }
+    }
+    /**
+     * 1*2*3*...*100 递归计算阶乘
+     */
+    public static int getSumThree (int i){
+        if (i == 1){
+            return i ;
+        } else {
+            return i * getSumThree (i - 1) ;
+        }
+    }
+}
