Java随记，

Java随记，

Runtime几点用途

public class testruntime {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Runtime rt = Runtime.getRuntime();

        System.out.println("处理器数量:"+rt.availableProcessors());
        System.out.println("可用内存:"+rt.freeMemory());    
    }

}

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Scanner读取文件内容

public class testScannerfile {

    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub

        Scanner sc = new Scanner(new File("test1.txt"));
        while(sc.hasNextLine()){
            System.out.println(sc.nextLine());
        }

    }

}

String CompareTo方法

其他更多string的方法查看java疯狂讲义249页。最好查看API

stringbuilder的几个方法
public class testSringbuilder {

public static void main(String[] args) {
    // TODO Auto-generated method stub

    StringBuilder str = new StringBuilder("hello ");
    //结尾添加
    str.append("w");
    //插入
    str.insert(7, "o");
    //替换
    str.replace(7, 8, "or");
    //反转
    str.reverse();
    //设置字符串的长度
    str.setLength(5);

    System.out.println(str);


}

}

Random几种简单用法
public class TestRand {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Random rand = new Random();//伪随机
        Random rand2 = new Random(System.currentTimeMillis());
        //生成随机数，可以是int，float，double等都可
        //生成0-10之间的整数
        System.out.println(rand.nextInt(10));

        System.out.println(rand2.nextInt(5));

        ThreadLocalRandom val = ThreadLocalRandom.current();

        System.out.println(val.nextDouble(2,5));



    }

}